Seed germination occurs over a period of time and this interval is dependent on the species, cultivar and environment. This interval can be as long as 7 to 14 days. This spread in time to emergence results in uneven maturity which presents problems for harvesting the crop. Certain horticultural crops such as tomatoes are harvested mechanically with the plants being sacrificed at the time of harvest. If the stand is not uniform, a large percent of the fruit is not marketable. In cereal crops, the producer must delay harvest until all of the crop is uniform or the crop must be swathed to promote ripening. There are distinct advantages to combining the crop directly. First, less energy is required as the swathing operation is negated. Under cool, wet conditions, it takes longer for the crop to dry down compared to a standing crop. Often a crop that is in a swath may undergo pre-harvest sprouting if conditions are wet. This results in a loss in grade and money. Also, some crops such as canola and wheat may shatter (seeds drop from the plant) while the producer is waiting for the crop to mature.
A period of controlled seed hydration in polyethylene glycol (PEG) or salt solutions (osmotic pruning) is currently used to enhance and synchronize seed germination of vegetable crops. Following treatment with PEG on salt solutions, the seeds must be dried to allow seeding with conventional seeders. In some cases priming of seeds may result in deterioration of seeds especially if the temperature is too warm. If the seeds are not planted immediately, they must be dried back to moisture contents for storage or they may rapidly deteriorate. If PEG is used to treat seeds it must be washed off the seeds prior to planting and storage.
Osmotic priming to enhance and synchronize seed germination is in many respects unsatisfactory. Generally speaking it is lengthy and inconvenient. Simpler, shorter and more efficient alternatives are required.